This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 5 |
| 4 | 18 |
| 5 | 97 |
| 6 | 600 |
| 7 | 4325 |
| 8 | 35280 |
| 9 | 322578 |
| 10 | 3265920 |
| 11 | 36288097 |
| 12 | 439084800 |
| 13 | 5748019800 |
| 14 | 80951270400 |
| 15 | 1220496081125 |
| 16 | 19615115520000 |
| 17 | 334764638243280 |
| 18 | 6046686277632000 |
| 19 | 115242726703426578 |